Knowledge organization system (KOS), concept system or concept scheme is the generic term used in knowledge organization for the selection of concepts with an indication of selected semantic relations.^[1] Despite their differences in type, coverage and application, all KOS aim to support the organization of knowledge and information to facilitate their management and retrieval.

KOS can be represented in can be expressed in RDF and RDFS as per the Simple Knowledge Organization System (SKOS) recommendation by W3C, which aims to enable the sharing and linking of KOS via the Web.^[2]

Many lists of KOS exist with BARTOC being the largest and most general one.

Examples of knowledge organization systems include:

• classification systems and schemes
• lists of subject headings
• authority files
• thesauri
• topic maps
• controlled vocabularies
• ontologies
• other systems of metadata

• Library and information science
• Library classification